Observation devices for observing a fluorescent image generated in accordance with emission of excitation light from a living body or the like have been used conventionally. In such observation devices, an image obtained by capturing a reflected image generated by illumination light and an image obtained by capturing the fluorescent image generated by the excitation light are superimposed. For example, the following Patent Literature 1 describes a configuration in which a balance between a fluorescent image and a reflected image is adjusted by superimposing image data of a binned fluorescent image and image data of a reflected image. Also, in the following Patent Literature 2, a process of creating an image of a fluorescent image by assigning data to which an estimated fluorescence yield or the like is added to a pixel value and outputting an observation image by superimposing the image and a reflected image is described.